1. Field of the Invention
The present invention relates to a plasma processing system for introducing a microwave into a plasma processing chamber through an annular waveguide having a plurality of slots provided on the side of the plasma processing chamber to generate plasma in the plasma processing chamber, and also relates to a surface processing method and a method of manufacturing an element, using the same.
2. Related Background Art
As to plasma processing systems using a microwave as an excitation source for generating plasma, there are known an etching system, an ashing system, a CVD system, a doping system and the like.
Semiconductor devices such as transistors, diodes and LSIs are manufactured by subjecting a semiconductor substrate (wafer) having a large number of semiconductor elements formed thereon to the various kinds of surface processings using a large number of systems such as the above-mentioned plasma processing system and the like.
The etching processing for an object to be processed using a microwave plasma etching system, for example, is carried out in the following manner. That is to say, etchant gas is introduced into a plasma processing chamber of the microwave plasma etching system and at the same time, the microwave energy is supplied thereto to excite and decompose the etchant gas to thereby etch away the surface of the object to be processed which is arranged within the plasma processing chamber.
In addition, the ashing processing for an object to be processed using a microwave plasma ashing system, for example, is carried out in the following manner. That is to say, ashing gas is introduced into a plasma processing chamber of the microwave plasma ashing system and at the same time, the microwave energy is supplied thereto to excite and decompose the ashing gas to thereby ash the surface of the object to be processed which is arranged within the plasma processing chamber.
Also, the film forming processing for an object to be processed using a microwave plasma CVD system, for example, is carried out in the following manner. That is to say, reactive gas is introduced into a plasma processing chamber of the microwave plasma CVD system and at the same time, the microwave energy is supplied thereto to excite and decompose the reactive gas to thereby deposit a film on the subject to be processed which is arranged within the plasma processing chamber.
Moreover, the doping processing for an object to be processed using a microwave plasma doping system, for example, is carried out in the following manner. That is to say, doping gas is introduced into a plasma processing chamber of the microwave plasma doping system and at the same time, the microwave energy is supplied thereto to excite and decompose the reactive gas to thereby dope the surface of the object to be processed which is arranged within the plasma processing chamber with desired impurities.
Since in the microwave plasma processing system, the microwave having a high frequency is used as the excitation source for the gas, the number of times of acceleration of electrons increases to increase the electron density and hence the gas molecules can be effectively ionized and excited. For this reason, the microwave plasma processing system has the advantage that the ionization efficiency, the excitation efficiency and decomposition efficiency of gas are all high and the high-quality processing can be therefore carried out at high speed even at low temperatures. In addition, since the microwave has the property of permeating dielectric, there is also offered the advantage that the plasma processing system can be constructed as being of an electrodeless discharge type so that the highly clean plasma processing can be made.
In order to further promote the high speed processing in such microwave plasma processing systems, the plasma processing system utilizing the electron cyclotron resonance (ECR) has also been made fit for practical use. The ECR is the phenomenon in which when the magnetic flux density is 87.5 mT, the electron cyclotron frequency at which the electrons turn round the line of magnetic force matches the frequency of 2.45 GHz which is general in the microwave and the electrons absorb the microwave resonantly to thereby be accelerated to generate the high-density plasma.
As one example of the microwave plasma processing systems, in recent years, there has been proposed a system employing an annular non-terminal waveguide as the apparatus for introducing uniformly and efficiently the microwave in which a plurality of linear slots are radially formed on a plate-like H face (refer to JP-A-10-233295). This microwave plasma processing system is shown in FIG. 5A, and its plasma generating mechanism is shown in FIGS. 5B and 5C. In these figures, reference numeral 901 designates a plasma processing chamber; reference numeral 902, an object to be processed; reference numeral 903, a supporting body for supporting the substrate 902; reference numeral 904, means for adjusting a temperature of the substrate 902; reference numeral 905, means for applying a high-frequency bias; reference numeral 906, means for introducing processing gas; reference numeral 907, exhaust means; reference numeral 908, means for adjusting an exhaust conductance; reference numeral 909, a dielectric member for separating therethrough the plasma processing chamber 901 from the atmospheric side; reference numeral 910, an annular non-terminal waveguide with slots for introducing the microwave into the plasma processing chamber 901 after permeation through the dielectric member 909; reference numeral 912, a microwave waveguide within the annular non-terminal waveguide 910; reference numeral 913, an E distributor for distributing the microwave introduced into the annular non-terminal waveguide 910 right and left; reference numeral 915, a slot; reference numeral 916, a surface wave which is introduced through the slots 915 to be propagated on the surface of the dielectric member 909; reference numeral 917, a surface standing wave which is generated due to the interference between the surface waves 916 introduced through the adjacent slots; 918, surface plasma which is generated due to the presence of the surface standing wave 917; and 919, bulk plasma which is generated due to the diffusion of the surface plasma 918.
The generation of the plasma and the processing thereby are carried out in the following manner. Air in the plasma processing chamber 901 is vacuum-exhausted through the exhaust means 907. Subsequently, plasma processing gas is introduced at predetermined flow rate into the plasma processing chamber 901 through the means 906 for introducing therethrough processing gas. Next, the means 908 for adjusting an exhaust conductance which is provided between the plasma processing chamber 901 and the exhaust means 907 is adjusted to hold the inside of the plasma processing chamber at a predetermined pressure. If necessary, the bias voltage is applied to the object 902 to be processed through the means 905 for applying a high-frequency bias.
The desired electric power is supplied from a microwave power source (not shown) to the plasma processing chamber 901 through the annular non-terminal waveguide 910. In this connection, the microwave which has been introduced into the annular non-terminal waveguide 910 is distributed right and left to be propagated through the waveguide 912 with a wavelength inside the waveguide longer than the wavelength in the free space. The microwaves obtained through the distribution interfere with each other to generate the standing wave 917 at intervals of one half the wavelength inside the waveguide.
The electrons are accelerated by the surface standing wave 917 which is generated in the plasma processing chamber 901 after permeation of the microwave through the dielectric member 909 to generate the surface plasma 918. In addition, the bulk plasma 919 is generated due to the diffusion of the surface plasma 918. The surface-wave interfered plasma (SIP) thus generated has the two-layer structure consisting of the surface plasma 918 and the bulk plasma 919. At this time, if the processing gas is introduced into the plasma processing chamber 901 through the means 906 for introducing therethrough processing gas, then the processing gas is excited by the high-density plasma thus generated to process the surface of the object 902 to be processed which is placed on the supporting body 903.
However, when the microwave is introduced into the plasma processing chamber in the above-mentioned system, there is encountered the problem that the uniformity of the microwave in a circumferential direction of the waveguide is reduced due to the change in conditions such as the pressure and the microwave electric power to reduce the uniformity of the generated plasma accordingly.